Partially fluroinated benzene derivatives, and liquid-crystalline medium

ABSTRACT

Partially fluorinated benzene derivatives of the formula I ##STR1## in which R, A 1 , A 2 , Q, Y, L 1 , L 2 , L 3  and m are as defined in claim 1, 
     are suitable as components of liquid-crystalline media.

This application is a continuation of application Ser. No. 08/549,706,filed Nov. 15, 1995 now abandoned.

The invention relates to partially fluorinated benzene derivatives ofthe formula I ##STR2## in which R is H, an alkyl or alkenyl radicalhaving 1 to 15 carbon atoms which is unsubstituted or monosubstituted byCN or CF₃ or at least monosubstituted by halogen, it also being possiblefor one or more CH₂ Groups in these radicals to be replaced, in eachcase independently of one another, by --O--, --S--, ##STR3## --CO--,--CO--O--, --O--CO-- or --O--CO--O-- in such a manner that O atoms arenot linked directly to one another,

A¹ and A² are each, independently of one another,

(a) a trans-1,4-cyclohexylene radical in which, in addition, one or morenonadjacent CH₂ groups may be replaced by --O-- and/or --S--,

(b) a 1,4-phenylene radical in which, in addition, one or two CH groupsmay be replaced by N,

(c) a radical from the group consisting of 1,4-cyclohexylene,1,4-bicyclo 2.2.2!octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl,

it being possible for the radicals (a) and (b) to be substituted by oneor two fluorine atoms,

Z¹ and Z² are each, independently of one another, --CO--O--, --O--CO--,--CH₂ O--, --OCH₂ --, --CH₂ CH₂ --, --CH═CH--, --C.tbd.C--or a singlebond, and one of the radicals Z¹ and Z² is alternatively --(CH₂)₄ -- or--CH═CH--CH₂ CH₂ --, and

Q is --CHF-- or --CF₂ --,

Y is an unsubstituted or halogen-substituted alkyl radical having 1-5carbon atoms,

L¹, L²

and L³ are each, independently of one another, H or F, and

M is 0, 1 or 2.

The invention furthermore relates to the use of these compounds ascomponents of liquid-crystalline media, and to liquid-crystal andelectrooptical display elements which contain the liquid-crystallinemedia according to the invention.

The compounds of the formula I can be used as components ofliquid-crystalline media, in particular for displays based on theprinciple of the twisted cell, the guest-host effect, the effect ofdeformation of aligned phases or the effect of dynamic scattering.

The invention had the object of finding novel, stable liquid-crystallineor mesogenic compounds which are suitable as components ofliquid-crystalline media and in particular have at the same timecomparatively low viscosity and relatively high dielectric anisotropy.

It has now been found that compounds of the formula I are eminentlysuitable as components of liquid-crystalline media. In particular, theyhave comparatively low viscosities. They can be used to obtain stableliquid-crystalline media which have a broad mesophase range andadvantageous values for the optical and dielectric anisotropy. Thesemedia furthermore have very good low-temperature behavior andextraordinarily low threshold voltages.

WO 91-00102 and DE-A 40 02 374 describe similar partially fluorinatedbenzene derivatives.

In view of the extremely wide variety of areas of application of suchcompounds of high Δε, however, it was desirable to have furthercompounds of high nematogeneity available which have propertiesprecisely tailored to the particular application.

In addition, the provision of the compounds of the formula I verygenerally considerably broadens the range of liquid-crystallinesubstances which are suitable, from various applicational points ofview, for the preparation of liquid-crystalline mixtures.

The compounds of the formula I have a broad field of applications.Depending on the choice of substituents, these compounds can be used asbase materials from which liquid-crystalline media are predominantlycomposed; however, it is also possible to add compounds of the formula Ito liquid-crystalline base materials from other classes of compound inorder, for example, to modify the dielectric and/or optical anisotropyof a dielectric of this type and/or to optimize its threshold voltageand/or viscosity.

In the pure state, the compounds of the formula I are colorless and formliquid-crystalline mesophases in a temperature range which is favorablylocated for electrooptical use. They are stable chemically, thermallyand to light.

The invention thus relates to the compounds of the formula I and to theuse of these compounds as components of liquid-crystalline media. Theinvention furthermore relates to liquid-crystalline media containing atleast one compound of the formula I, and to liquid-crystal displayelements, in particular electro-optical display elements, which containmedia of this type.

In the compounds of the formulae above and below, m is preferably 0. Yis preferably an unsubstituted or halogen-substituted methyl, ethyl, orpropyl radical. Halogen is preferably fluorine.

Y is preferably CH₃, CH₂ CH₃, CHF₂, CH₂ CHF₂, CH₂ CF₃, CF₂ --CHF₂ orCF₃.

Q--Y is preferably CHF--CHF₂, CF₂ --CH₂ --CF₃ or CF₂ --CH₃, furthermoreCF₂ --CH₂ --CHF₂, CHF--CF₂ --CHF₂ or CF₂ --CH₂ --CHF₂.

L³ is preferably F and L¹ and L² are H or F. Particular preference isgiven to compounds in which L¹⁻³ are fluorine.

R is preferably alkyl, furthermore alkoxy. A¹ and/or A² are preferablyPhe, Cyc, Che, Pyr or Dio. The compounds of the formula I preferablycontain not more than one of the radicals Bi, Pyd, Pyr, Dio or Dit.

Preference is also given to compounds of the formula I and allsubformulae in which A¹ and A² are 1,4-phenylene which ismonosubstituted or disubstituted by F or monosubstituted by CN. Theseare, in particular, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene and3,5-difluoro-1,4phenylene, and 2cyano-1,4-phenylene and3-cyano-1,4-phenylene.

Z¹ and Z² are preferably a single bond, --CO--O--, --O--CO-- and --CH₂CH₂ --, and secondarily preferably --CH₂ O-- and --OCH₂ --.

If one of the radicals Z¹ and Z² is --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --,the other radical Z¹ or Z² (if present) is preferably a single bond.

If R is an alkyl radical and/or an alkoxy radical, this may bestraight-chain or branched. It is preferably straight-chain, has 2, 3,4, 5, 6 or 7 carbon atoms and is accordingly preferably ethyl, propyl,butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxyor heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy,undecoxy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl),2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl,2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonylor 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R is an alkyl radical in which one CH₂ group has been replaced by--CH═CH--, this may be straight-chain or branched. It is preferablystraight-chain and has 2 to 10 carbon atoms. Accordingly, it is inparticular vinyl, prop-1- or prop-2-enyl, but-1-, 2- or but-3-enyl,pent-1-, 2-, 3- or pent-4-enyl, hex-1-, 2-, 3-, 4- or hex-5-enyl,hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- oroct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, or dec-1-, 2-,3-, 4-, 5-, 6-, 7-, 8- or dec -9-enyl.

If R is an alkyl radical in which one CH₂ group has been replaced by--O-- and one has been replaced by --CO--, these are preferablyadjacent. These thus contain an acyloxy group --CO--O-- or anoxycarbonyl group --O--CO--. These are preferably straight-chain andhave 2 to 6 carbon atoms.

Accordingly, they are in particular acetyloxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl,2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl,3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

If R is an alkyl radical in which one CH₂ group has been replaced byunsubstituted or substituted --CH═CH-- and an adjacent CH₂ group hasbeen replaced by CO or CO--O or O--CO--, this may be straight-chain orbranched. It is preferably straight-chain and has 4 to 13 carbon atoms.Accordingly, it is in particular acryloyloxymethyl, 2-acryloyloxyethyl,3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl,6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl,9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl,2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxbutyl,5-methacryloyloxypentyl, 6-methacryloyloxyhexyl,7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or9-methacryloyloxynonyl.

If R is an alkyl or alkenyl radical which is monosubstituted by CN orCF₃, this radical is preferably straight-chain and the substitution isby CN or CF₃ in the ω-position.

If R is an alkyl or alkenyl radical which is at least monosubstituted byhalogen, this radical is preferably straight-chain and halogen ispreferably F or Cl. In the case of multiple substitution, halogen ispreferably F. The resulting radicals also include perfluorinatedradicals. In the case of monosubstitution, the fluorine or chlorinesubstituent can be in any desired position, but is preferably in theω-position.

Compounds of the formula I which contain wing groups R which aresuitable for poly addition reactions are suitable for the preparation ofliquid-crystalline polymers.

Compounds of the formula I containing branched wing groups R mayoccasionally be of importance due to better solubility in customaryliquid-crystalline base materials, but in particular as chiral dopes ifthey are optically active. Smectic compounds of this type are suitableas components for ferroelectric materials.

Compounds of the formula I having S_(A) phases are suitable, forexample, for thermally addressed displays.

Branched groups of this type generally contain not more than one chainbranch. Preferred branched radicals R are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy,1-methylhexoxy and 1-methylheptoxy.

If R is an alkyl radical in which two or more CH₂ groups have beenreplaced by --O-- and/or --CO--O--, this may be straight-chain orbranched. It is preferably branched and has 3 to 12 carbon atoms.Accordingly, it is in particular biscarboxymethyl, 2,2-biscarboxyethyl,3,3-biscarboxypropyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl,6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl,9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis(methoxycarbonyl)methyl,2,2-bis(methoxycarbonyl) ethyl, 3,3-his (methoxycarbonyl)propyl, 4,4-bis(methoxycarbonyl) butyl, 5,5-bis (methoxycarbonyl)pentyl, 6,6bis(methoxycarbonyl) hexyl, 7,7his (methoxycarbonyl)heptyl, 8,8bis(methoxycarbonyl) octyl, bis(ethoxycarbonyl)methyl,2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl,4,4-bis(ethoxycarbonyl)butyl or 5,5-bis(ethoxycarbonyl)hexyl.

Compounds of the formula I which contain wing groups R which aresuitable for polycondensations are suitable for the preparation ofliquid-crystalline polycondensates.

Formula I covers the racemates of these compounds and the opticalantipodes, and mixtures thereof.

Of these compounds of the formula I and the subformulae, preference isgiven to those in which at least one of the radicals present therein hasone of the preferred meanings indicated.

In the compounds of the formula I, preferred stereoisomers are those inwhich the rings Cyc and piperidine are trans-1,4-disubstituted. Those ofthe abovementioned formulae which contain one or more groups Pyd, Pyrand/or Dio in each case cover the two 2,5-positional isomers.

Preferred smaller groups of compounds are those of the subformulae I1 toI15: ##STR4##

Particular preference is given to compounds of the formulae I1, I2, I3,I5, I6 and I9.

The invention likewise relates to compounds of the formula ##STR5##

The compounds of the formula I are prepared by methods known per se, asdescribed in the literature (for example in the standard works, such asHouben-Weyl, Methoden der Organischen Chemie Methods of OrganicChemistry), Georg-Thieme-Verlag, Stuttgart, Vol. IX, pp. 867 ff.), to beprecise under reaction conditions which are known and suitable for saidreactions. Use may also be made here of variants which are known per se,but are not described here in greater detail.

The compounds according to the invention can be prepared, for example,by metalating a compound of the formula II, ##STR6## in which R, A¹, A²,Z¹, Z², L¹, L², L³ and m are as defined above, in accordance with thereaction scheme below, and subsequently reacting the product with asuitable electrophile: ##STR7##

The compounds of the formula I in which Q--Y is CHF--CF₃ are obtainablefrom the resultant phenol by known methods, for example by reacting thephenol with CF₃ --CHO and HF. ##STR8##

Compounds of the formula I in which Q--Y CF₂ -alkyl can be prepared, forexample, as follows. ##STR9##

Further synthetic methods are apparent to the person skilled in the art.For example, appropriately 5-substituted 1,3-difluorobenzene compoundsor monofluorinated analogues (L² ═H) can be converted, in accordancewith the above scheme, into the 1,3-difluoro compounds ormonofluorinated analogues (L² ═H), and the radical R--(A¹ --Z¹)_(m) --A²--Z² -- subsequently introduced by reactions customary in liquid-crystalchemistry (for example esterification, etherification or coupling, forexample as described in the article by E. Poetsch, Kontakte (Darmstadt)1988 (2), p. 15).

Compounds of the formula II can be prepared, for example, by thefollowing synthetic schemes: ##STR10##

The starting materials are either known or can be prepared analogouslyto known compounds.

Esters of the formula I can also be obtained by esterification ofcorresponding carboxylic acids (or reactive derivatives thereof) usingalcohols or phenols (or reactive derivatives thereof) or by the DCCmethod (DCC=dicyclohexylcarbodiimide).

The corresponding carboxylic acids and alcohols or phenols are known orcan be prepared analogously to known methods.

In a further process for the preparation of the compounds of the formulaI, an aryl halide is reacted with an olefin in the presence of atertiary amine and in the presence of a palladium catalyst (cf. R. F.Heck, Acc. Chem. Res. 12 (1979) 146). Examples of suitable aryl halidesare chlorides, bromides and iodides, in particular bromides and iodides.The tertiary amines necessary for the success of the coupling reaction,such as, for example, triethylamine, are also suitable as solvent.Examples of suitable palladium catalysts are palladium salts, inparticular Pd(II) acetate, with organic phosphorus (III) compounds, suchas, for example, triarylphosphines. This reaction can be carried out inthe presence or absence of an inert solvent at temperatures betweenabout 0° and 150°, preferably between 20° and 100°; examples of suitablesolvents are nitriles, such as acetonitrile, or hydrocarbons, such asbenzene or toluene. The aryl halides and olefins employed as startingmaterials are frequently commercially available or can be prepared byprocesses known from the literature, for example by halogenation ofcorresponding parent compounds or by elimination reactions oncorresponding alcohols or halides.

In this way, it is possible to prepare, for example, stilbenederivatives. The stilbenes can furthermore be prepared by reacting a4-substituted benzaldehyde with a corresponding phosphorus ylide by theWittig method. However, it is also possible to prepare tolans of theformula I by employing monosubstituted acetylene in place of the olefin(Synthesis 627 (1980) or Tetrahedron Lett. 27, 1171 (1986)).

A further way of coupling aromatic compounds is to react aryl halideswith aryltin compounds. These reactions are preferably carried out withaddition of a catalyst, such as, for example, a palladium(0) complex, ininert solvents, such as hydrocarbons, at high temperatures, for examplein boiling xylene, under a protective gas.

Coupling reactions of alkynyl compounds with aryl halides can be carriedout analogously to the process described by A. O. King, E. Negishl, F.J. Villani and A. Silveira in J. Org. Chem. 43, 358 (1978).

Tolans of the formula I can also be prepared via theFritsch-Buttenberg-Wiecheil rearrangement (Ann. 279, 319, 1984), inwhich 1,1-diaryl-2-haloethylenes are rearranged in the presence ofstrong bases to give diarylacetylenes.

Tolans of the formula I can also be prepared by brominating thecorresponding stilbenes followed by dehydrohalogenation. Use can also bemade here of variants of these reactions which are known per se, are notdescribed here in greater detail.

Ethers of the formula I can be obtained by etherification ofcorresponding hydroxyl compounds, preferably corresponding phenols, thehydroxyl compound expediently first being converted into a correspondingmetal derivative, for example into the corresponding alkali metalalkoxide or alkali metal phenoxide by treatment with NaH, NaNH₂, NaOH,KOH, Na₂ CO₃ or K₂ CO₃. This metal derivative can then be reacted withthe appropriate alkyl halide, sulfonate or dialkyl sulfate, expedientlyin an inert solvent, such as, for example, acetone, 1,2-dlmethoxyethane,DMF or dimethyl sulfoxide, or alternatively with an excess of aqueous oraqueous-alcoholic NaOH or KOH at temperatures between about 20° and 100°C.

The starting materials are either known or can be prepared analogouslyto known compounds.

The preferred trans-isomers can be prepared by isomerization methodsknown from the literature. The precursors where R⁰ ═H which may beobtained are converted into the compounds of the formula I' entirelyanalogously to the precursors of the compounds of the formula I byintroduction of the radical --Y--.

The aldehydes can be obtained by Heck reaction of appropriatelysubstituted 1-bromo-3-fluorobenzene derivatives with allyl alcohol.

The synthesis of some particularly preferred compounds is shown below ingreater detail: ##STR11##

The liquid-crystalline media according to the invention preferablycontain 2 to 40, in particular 4 to 30, components as furtherconstituents besides one or more compounds according to the invention.These media very particularly preferably contain 7 to 25 componentsbesides one or more compounds according to the invention. These furtherconstituents are preferably selected from nematic or nematogenic(monotropic or isotropic) substances, in particular substances from theclasses of the azoxybenzenes, benzylideneanilines, biphenyls,terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl estersof cyclohexanecarboxylic acid, phenyl or cyclohexyl esters ofcyclohexylbenzoic acid, phenyl or cyclohexyl esters ofcyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoicacid, of cyclohexanecarboxylic acid and ofcyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes,1,4-biscyclohexyl-benzenes, 4,4'-biscyclohexylbiphenyls, phenyl- orcyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- orcyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes,1,2-diphenylethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cyclohexylethanes,1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes,1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes,optionally halogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids. The 1,4-phenylene groups in these compoundsmay also be fluorinated.

The most important compounds suitable as further constituents of mediaaccording to the invention can be characterized by the formulae 1, 2, 3,4 and 5:

    R'--L--E--R"                                               1

    R'--L--COO--E--R"                                          2

    R'--L--OOC--E--R"                                          3

    R'--L--CH.sub.2 CH.sub.2 --E--R"                           4

    R'--L--C.tbd.C--E--R"                                      5

In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical ordifferent, are in each case, independently of one another, a bivalentradical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-,-Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images,where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc istrans-1,4-cyclohexylene or 1,4-cyclohexylene, Pyr is pyrimidine-2,5-diylor pyridine-2,5-diyl,-Dio is 1,3-dioxane-2,5-diyl and G is2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-Z,5-diyl, pyridine-2,5-diyl or1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. E ispreferably Cyc, Phe or Phe-Cyc. The media according to the inventionpreferably contain one or more components selected from the compounds ofthe formulae 1, 2, 3, 4 and 5 in which L and E are selected from thegroup consisting of Cyc, Phe and Pyr and simultaneously one or morecomponents selected from the compounds of the formulae 1, 2, 3, 4 and 5in which one of the radicals L and E is selected from the groupconsisting of Cyc, Phe and Pyr and the other radical is selected fromthe group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and-G-Cyc-, and optionally one or more components selected from thecompounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and Eare selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe-and -G-Cyc-.

In a smaller subgroup of compounds of formulae 1, 2, 3, 4 and 5, R' andR" are each, independently of one another, alkyl, alkenyl, alkoxy,alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. Thissmaller subgroup is referred to as group A below, and the compounds arelabeled with the subformulae 1a, 2a, 3a, 4a and 5a. In most of thesecompounds, R' and R" are different from one another, one of theseradicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller subgroup of the compounds of the formulae 1, 2, 3, 4and 5, known as group B, R" is --F, --Cl, --NCS or --(O)_(i) CH₃₋(k+1)F_(k) Cl₁, where i is 0 or 1 and k+1 is 1, 2 or 3; the compounds inwhich R" has this meaning are labeled with the subformulae 1b, 2b, 3b,4b and 5b. Particular preference is given to the compounds of thesubformulae 1b, 2b, 3b, 4b and 5b in which R" is --F, --Cl, --NCS,--CF₃, --OCHF₂ or --OCF₃.

In the compounds of the subformulae 1b, 2b, 3b, 4b and 5b, R' is asdefined for the compounds of the subformulae 1a-5a and is preferablyalkyl, alkenyl, alkoxy or alkoxyalkyl.

In a further smaller subgroup of the compounds of the formulae 1, 2, 3,4 and 5, R" is --CN; this subgroup is known as group C below, and thecompounds of this subgroup are accordingly described by subformulae 1c,2c, 3c, 4c and 5c. In the compounds of the subformulae 1c, 2c, 3c, 4cand 5c, R' is as defined for the compounds of the subformulae 1a-5a andis preferably alkyl, alkoxy or alkenyl.

In addition to the preferred compounds of groups A, B and C, othercompounds of the formulae 1, 2, 3, 4 and 5 with other variants of theproposed substituents are also common. All these substances can beobtained by methods known from the literature or analogously thereto.

The media according to the invention preferably contain one or morecompounds selected from group A and/or group B and/or group C inaddition to compounds of the formula I according to the invention. Theproportions by weight of the compounds from these groups in the mediaaccording to the invention are preferably

Group A: from 0 to 90%, preferably from 20 to 90%, in particular from 30to 90%

Group B: from 0 to 80%, preferably from 10 to 80%, in particular from 10to 65%

Group C: from 0 to 80%, preferably from 5 to 80%, in particular from 5to 50%

the sum of the proportions by weight of the compounds from groups Aand/or B and/or C present in the respective media according to theinvention preferably being from 5 to 90% and in particular from 10 to90%.

The media according to the invention preferably contain 1 to 40%, inparticular preferably 5 to 30%, of compounds according to the invention.Further preferred media are those which contain more than 40%, inparticular 45 to 90%, of compounds according to the invention. The mediapreferably contain three, four or five compounds according to theinvention.

The media according to the invention are prepared in a manner which iscustomary per se. In general, the components are dissolved in oneanother, expediently at elevated temperature. By means of suitableadditives, the liquid-crystalline phases can be modified in accordancewith the invention in such a manner that they can be used in all typesof liquid-crystal display elements which have been disclosed hitherto.Additives of this type are known to those skilled in the art and aredescribed in detail in the literature (H. Kelker/R. Hatz, Handbook ofLiquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroicdyes can be added for the production of colored guest-host systems, orsubstances can be added to modify the dielectric anisotropy, theviscosity and/or the orientation of the nematic phases.

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by means of acronyms, thetransformation into chemical formulae being carried out in accordancewith Tables A and B below. All radicals C_(n) H_(2n+1) and C_(m)H_(2m+1) are straight-chain alkyl radicals having n or m carbon atomsrespectively. The coding in Table B is self-evident. In Table A, onlythe acronym for the parent structure is shown. In individual cases, theacronym for the parent structure is followed, separated by a hyphen, bya code for the substituents R¹, R², L¹ and L² :

    ______________________________________                                        Code for R.sup.1,                                                             R.sup.2, L.sup.1, L.sup.2                                                             R.sup.1           R.sup.2    L.sup.1                                                                           L.sup.2                              ______________________________________                                        nm      C.sub.n H.sub.2n+1                                                                              C.sub.m H.sub.2m+1                                                                       H   H                                    nOm     C.sub.n H.sub.2n+1                                                                              OC.sub.m H.sub.2m+1                                                                      H   H                                    nO.m    OC.sub.n H.sub.2n+1                                                                             C.sub.m H.sub.2m+1                                                                       H   H                                    n       C.sub.n H.sub.2n+1                                                                              CN         H   H                                    nN.F    C.sub.n H.sub.2n+1                                                                              CN         H   F                                    nF      C.sub.n H.sub.2n+1                                                                              F          H   H                                    nOF     OC.sub.n H.sub.2n+1                                                                             F          H   H                                    nCl     C.sub.n H.sub.2n+1                                                                              Cl         H   H                                    nF.F    C.sub.n H.sub.2n+1                                                                              F          H   F                                    nF.F.F  C.sub.n H.sub.2n+1                                                                              F          F   F                                    nCF.sub.3                                                                             C.sub.n H.sub.2n+1                                                                              CF.sub.3   H   H                                    nOCF.sub.3                                                                            C.sub.n H.sub.2n+1                                                                              OCF.sub.3  H   H                                    nOCF.sub.2                                                                            C.sub.n H.sub.2n+1                                                                              OCHF.sub.2 H   H                                    nS      C.sub.n H.sub.2n+1                                                                              NCS        H   H                                    rVsN    C.sub.r H.sub.2r+1 --CH═CH--C.sub.s H.sub.2s --                                             CN         H   H                                    rEsN    C.sub.r H.sub.2r+1 --O--C.sub.s H.sub.2s --                                                     CN         H   H                                    nAm     C.sub.n H.sub.2n+1                                                                              COOC.sub.m H.sub.2m+1                                                                    H   H                                    ______________________________________                                    

                  TABLE A                                                         ______________________________________                                         ##STR12##                                                                     ##STR13##                                                                     ##STR14##                                                                     ##STR15##                                                                     ##STR16##                                                                     ##STR17##                                                                     ##STR18##                                                                     ##STR19##                                                                     ##STR20##                                                                     ##STR21##                                                                     ##STR22##                                                                     ##STR23##                                                                     ##STR24##                                                                     ##STR25##                                                                     ##STR26##                                                                     ##STR27##                                                                     ##STR28##                                                                     ##STR29##                                                                     ##STR30##                                                                     ##STR31##                                                                     ##STR32##                                                                     ##STR33##                                                                     ##STR34##                                                                     ##STR35##                                                                     ##STR36##                                                                     ##STR37##                                                                    ______________________________________                                    

                  TABLE B                                                         ______________________________________                                         ##STR38##                                                                     ##STR39##                                                                     ##STR40##                                                                     ##STR41##                                                                     ##STR42##                                                                     ##STR43##                                                                     ##STR44##                                                                     ##STR45##                                                                     ##STR46##                                                                     ##STR47##                                                                     ##STR48##                                                                     ##STR49##                                                                     ##STR50##                                                                     ##STR51##                                                                     ##STR52##                                                                     ##STR53##                                                                     ##STR54##                                                                     ##STR55##                                                                     ##STR56##                                                                     ##STR57##                                                                     ##STR58##                                                                     ##STR59##                                                                    ______________________________________                                    

The examples below are intended to illustrate the invention withoutrepresenting a limitation. Above and below, percentages are by weight.All temperatures are given in degrees celcius. m.p. denotes meltingpoint, c.p.=clearing point. Furthermore, C=crystalline state, N=nematicphase, S=smectic phase, I=isotropic phase. The numbers between thesesymbols indicate the transition temperatures. An denotes opticalanisotropy (589 nm, 20° C.) and the viscosity (mm² /sec) was determinedat 20° C.

"Conventional work-up" means that water is added if desired, the mixtureis extracted with dichloromethane, diethyl ether or toluene, the organicphase is separated off, dried and evaporated, and the product ispurified by distillation under reduced pressure or crystallizationand/or chromatography. The following abbreviations are used:

DAST Diethylaminosulfur trifluoride

DMEU 1,3-Dimethyl-2-imidazoladinone

POT Potassium tert-butoxide

THF Tetrahydrofuran

pTSOH p-Toluenesulfonic acid

EXAMPLE 1 ##STR60##

0.25 mol of I and 0.025 mol of sodium hydride (60% dispersion in oil)are dissolved in 500 ml of THF, the mixture is stirred for 15 hours andevaporated, and the residue is transferred into an autoclave. After1,000 ml of DMEU have been added, 0.3 mol of 1-bromo-2,2-difluoretheneare passed into the mixture, which has been cooled to -5° C. After themixture has been stirred at 100° C. for 15 hours, the reaction solutionis allowed to cool to room temperature and is poured into 2 l of water.The mixture is extracted with methyl tert-butyl ether. The combinedorganic extracts are evaporated, and the residue is chromatographed on asilica-gel polymer using n-hexane as eluent. ##STR61##

0.5 mol of aluminum shot and 0.05 mol of HgCl₂ and the intermediateobtained from Example 1a) are introduced at 0° C. into a mixture of 250ml of THF and 250 ml of methanol. The mixture is stirred at 0° C. for 24hours and at room temperature for a further 24 hours. The mixture issubsequently filtered, and 200 ml if petroleum ether and 1 l of waterare added to the filtrate. The organic phase is separated off, washed anumber of times with 5N hydrochloric acid and evaporated. The residue ischromatographed on a silica-gel polymer using n-hexane. The eluate isevaporated in a rotary evaporator, and the residue is recrystallizedfrom ethanol.

The following compounds of formula ##STR62## are prepared analogously:

    ______________________________________                                        R      (A.sup.1 -Z.sup.1).sub.m -A.sup.2 -Z.sup.2                                                    L.sup.1                                                                              L.sup.2                                                                            L.sup.3                                                                            Y                                     ______________________________________                                        C.sub.2 H.sub.5                                                                       ##STR63##      F      F    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR64##      F      F    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR65##      F      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR66##      F      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR67##      H      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR68##      H      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR69##      F      F    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR70##      F      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR71##      H      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR72##      F      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR73##      H      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR74##      F      F    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR75##      F      F    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR76##      F      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR77##      F      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR78##      H      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR79##      H      H    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR80##      F      F    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR81##      F      F    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR82##      F      H    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR83##      F      H    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR84##      H      H    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR85##      H      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR86##      F      F    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR87##      F      F    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR88##      F      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR89##      F      H    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR90##      H      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR91##      H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR92##      F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR93##      F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR94##      H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR95##      F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR96##      H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR97##      F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR98##      F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR99##      F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR100##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR101##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR102##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR103##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR104##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR105##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR106##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR107##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR108##     H      H    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR109##     F      F    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR110##     F      F    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR111##     F      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR112##     F      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR113##     H      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR114##     H      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR115##     F      F    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR116##     F      F    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR117##     F      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR118##     H      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR119##     F      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR120##     H      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR121##     F      F    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR122##     F      F    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR123##     F      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR124##     F      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR125##     H      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR126##     H      H    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR127##     F      F    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR128##     F      F    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR129##     F      H    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR130##     F      H    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR131##     H      H    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR132##     H      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR133##     F      F    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR134##     F      F    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR135##     F      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR136##     F      H    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR137##     H      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR138##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR139##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR140##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR141##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR142##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR143##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR144##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR145##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR146##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR147##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR148##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR149##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR150##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR151##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR152##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR153##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR154##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR155##     H      H    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR156##     F      F    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR157##     F      F    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR158##     F      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR159##     F      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR160##     H      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR161##     H      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR162##     F      F    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR163##     F      F    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR164##     F      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR165##     H      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR166##     F      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR167##     H      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR168##     F      F    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR169##     F      F    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR170##     F      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR171##     F      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR172##     H      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR173##     H      H    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR174##     F      F    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR175##     F      F    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR176##     F      H    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR177##     F      H    H    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR178##     H      H    F    CH.sub.3                              n-C.sub.6 H.sub.13                                                                    ##STR179##     H      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR180##     F      F    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR181##     F      F    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR182##     F      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR183##     F      H    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR184##     H      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR185##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR186##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR187##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR188##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR189##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR190##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR191##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR192##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR193##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR194##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR195##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR196##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR197##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR198##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR199##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR200##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR201##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR202##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.6 H.sub.13                                                                    ##STR203##     H      H    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR204##     F      F    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR205##     F      F    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR206##     F      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR207##     F      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR208##     H      H    F    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR209##     H      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR210##     F      F    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR211##     F      F    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR212##     F      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR213##     H      H    F    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR214##     F      H    H    CH.sub.3                              n-C.sub.3 H.sub.7                                                                     ##STR215##     H      H    H    CH.sub.3                              n-C.sub.4 H.sub.9                                                                     ##STR216##     F      F    F    CH.sub.3                              n-C.sub.4 H.sub.9                                                                     ##STR217##     F      F    H    CH.sub.3                              n-C.sub.4 H.sub.9                                                                     ##STR218##     F      H    F    CH.sub.3                              n-C.sub.4 H.sub.9                                                                     ##STR219##     F      H    H    CH.sub.3                              n-C.sub.4 H.sub.9                                                                     ##STR220##     H      H    F    CH.sub.3                              n-C.sub.4 H.sub.9                                                                     ##STR221##     H      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR222##     F      F    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR223##     F      F    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR224##     F      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR225##     F      H    H    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR226##     H      H    F    CH.sub.3                              n-C.sub.5 H.sub.11                                                                    ##STR227##     H      H    H    CH.sub.3                              C.sub.2 H.sub.5                                                                       ##STR228##     F      F    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR229##     F      F    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR230##     F      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR231##     F      H    H    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR232##     H      H    F    CH.sub.2 CH.sub.3                     C.sub.2 H.sub.5                                                                       ##STR233##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR234##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR235##     F      F    H    CH.sub.2 CH.sub.2                     n-C.sub.3 H.sub.7                                                                     ##STR236##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR237##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR238##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.3 H.sub.7                                                                     ##STR239##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.4 H.sub.9                                                                     ##STR240##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.4 H.sub.9                                                                     ##STR241##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.4 H.sub.9                                                                     ##STR242##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.4 H.sub.9                                                                     ##STR243##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.4 H.sub.9                                                                     ##STR244##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.4 H.sub.9                                                                     ##STR245##     H      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR246##     F      F    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR247##     F      F    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR248##     F      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR249##     F      H    H    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR250##     H      H    F    CH.sub.2 CH.sub.3                     n-C.sub.5 H.sub.11                                                                    ##STR251##     H      H    H    CH.sub.2 CH.sub.3                     ______________________________________                                    

EXAMPLE 2 ##STR252##

0.04 mol of 20% solution of diisobutylaluminum hydride in n-hexane isadded dropwise at -70° C. under N₂ with stirring to a solution of 0.04mol of 4-bromophenyl trifluoroacetate in 100 ml of hexane. The mixtureis slowly warmed to room temperature, stirred overnight and carefullyhydrolyzed with ice cooling. The organic phase is separated off, and theaqueous phase is extracted with methyl tert-butyl ether. The combinedorganic extracts are washed with water, dried over sodium sulfate,filtered and evaporated in a rotary evaporator. The residue is dissolvedin 20 ml of dichloromethane, and 0.0375 mol of DAST are added dropwisewith ice cooling. The mixture is stirred at room temperature for 6 hoursand then refluxed for 15 hours. The mixture is subsequently introduceddropwise into approx. 50 ml of ice water. The organic phase is separatedoff, and the aqueous phase is extracted a number of times withdichloromethane. The product is finally subjected to conventionalwork-up. ##STR253##

0.06 mol of p-trans- 4-pentylcyclohexyl!-2-fluorophenylboronic acid in60 ml of toluene are added to 4.8 g of NaOH in 30 ml of water, and themixture is stirred at 45° C. for 0.5 hour. 0.03 mol of1-(1,2,2,2-tetrafluoroethoxy)-4-bromobenzene and 0.7 g oftetrakis(triphenylphosphine)palladium(0) are added to the solution, andthe mixture is stirred at 100° C. overnight. The mixture is cooled toroom temperature, and the organic phase is separated off. The solvent isremoved in a rotary evaporator, and the residue is recrystallized fromn-hexane using petroleum ether.

The following compounds of the formula ##STR254## are preparedanalogously:

    ______________________________________                                        R          (A.sup.1 -Z.sup.1).sub.m -A.sup.2 -Z.sup.2                                                 L.sup.1                                                                             L.sup.2                                                                           L.sup.3                                     ______________________________________                                        n-C.sub.6 H.sub.13                                                                        ##STR255##  H     H   H                                           n-C.sub.6 H.sub.13                                                                        ##STR256##  H     H   F                                           n-C.sub.6 H.sub.13                                                                        ##STR257##  F     H   H                                           n-C.sub.6 H.sub.13                                                                        ##STR258##  F     F   H                                           n-C.sub.6 H.sub.13                                                                        ##STR259##  F     H   F                                           n-C.sub.6 H.sub.13                                                                        ##STR260##  F     F   F                                           CH.sub.3 CHCH                                                                             ##STR261##  F     F   F                                           CH.sub.2 CH                                                                               ##STR262##  F     F   F                                           C.sub.2 H.sub.5                                                                           ##STR263##  H     H   H                                           C.sub.2 H.sub.5                                                                           ##STR264##  H     H   F                                           C.sub.2 H.sub.5                                                                           ##STR265##  F     H   H                                           C.sub.2 H.sub.5                                                                           ##STR266##  F     F   H                                           C.sub.2 H.sub.5                                                                           ##STR267##  F     H   F                                           C.sub.2 H.sub.5                                                                           ##STR268##  F     F   F                                           n-C.sub.3 H.sub.7                                                                         ##STR269##  H     H   H                                           n-C.sub.3 H.sub.7                                                                         ##STR270##  H     H   F                                           n-C.sub.3 H.sub.7                                                                         ##STR271##  F     H   H                                           n-C.sub.3 H.sub.7                                                                         ##STR272##  F     F   H                                           n-C.sub.3 H.sub.7                                                                         ##STR273##  F     H   F                                           n-C.sub.3 H.sub.7                                                                         ##STR274##  F     F   F   C104 l; Δn = +0.102; Δ.e                                          psilon. = 20.92                         n-C.sub.5 H.sub.11                                                                        ##STR275##  H     H   F                                           n-C.sub.5 H.sub.11                                                                        ##STR276##  F     H   H                                           n-C.sub.5 H.sub.11                                                                        ##STR277##  F     F   H                                           n-C.sub.5 H.sub.11                                                                        ##STR278##  F     H   F                                           n-C.sub.5 H.sub.11                                                                        ##STR279##  F     F   F   C98 l; Δn = +0.116; Δ.ep                                          silon. = 22.22                          ______________________________________                                    

EXAMPLE 3 ##STR280## Step 3.1 ##STR281##

1.0 mol of sodium hydride are suspended in 200 ml of THF at 0° C. in anitrogen atmosphere. 1.0 ml of 4-bromo-2,6-dilfluorophenol, dissolved in400 ml of THF, is added dropwise to the suspension. The mixture isallowed to warm to room temperature, is stirred for a further 0.5 hour,is filtered and is evaporated in a rotary evaporator. The residue isdissolved in 150 ml of toluene and re-evaporated until crystals form.The product recrystallized from petroleum ether.

Step 3.2 ##STR282##

0.2 mol of 4-bromo-2,6-difluorophenol and 0.02 mol of sodium4-bromo-2,6-difluorophenoxide are dissolved in 400 ml of DMEU. 0.66 molof pentafluoropropene are introduced into the solution at 5° C. Thesolution is subsequently heated at 120° C. for 16 hours in an autoclave,allowed to cool to room temperature and poured into water. The organicphase is separated off and subjected to conventional work-up.

Step 3.3 ##STR283##

A solution comprising 0.02 mol of4-bromo-2,6-difluoro-1,1,3,3,3-pentafluoropropyl ether in 85 ml of THFis heated to 60° C., and 0.02 mol of p-trans-4-propyleyclohexyl!-2,6-difluorophenylboronic acid and a solutioncomprising 0.02 mol of potassium dihydrogenphosphate and 0.04 mol ofsodium hydrogenphosphate and 40 ml of water are added. After 0.33 g oftetrakis(triphenylphosphine)palladium (0) has been added, the mixture isstirred at 70° C. overnight. The reaction mixture is subsequentlyallowed to cool to room temperature. The organic phase is separated offand subjected to conventional work-up.

The following compounds of the formula ##STR284## are preparedanalogously:

    ______________________________________                                        R           (A.sup.1 -Z.sup.1).sub.m -A.sup.2 -Z.sup.2                                                       L                                              ______________________________________                                        CH.sub.3                                                                                   ##STR285##        H                                              CH.sub.3                                                                                   ##STR286##        F                                              C.sub.2 H.sub.5                                                                            ##STR287##        H                                              C.sub.2 H.sub.5                                                                            ##STR288##        F                                              n-C.sub.3 H.sub.7                                                                          ##STR289##        H                                              n-C.sub.4 H.sub.9                                                                          ##STR290##        H                                              n-C.sub.4 H.sub.9                                                                          ##STR291##        F                                              n-C.sub.5 H.sub.11                                                                         ##STR292##        H                                              n-C.sub.5 H.sub.11                                                                         ##STR293##        F                                              n-C.sub.6 H.sub.13                                                                         ##STR294##        H                                              n-C.sub.6 H.sub.13                                                                         ##STR295##        F                                              H.sub.2 CCH                                                                                ##STR296##        H                                              H.sub.2 CCH                                                                                ##STR297##        F                                              H.sub.3 CCHCH                                                                              ##STR298##        H                                              H.sub.3 CCHCH                                                                              ##STR299##        F                                              C.sub.2 H.sub.5                                                                            ##STR300##        H                                              C.sub.2 H.sub.5                                                                            ##STR301##        F                                              n-C.sub.3 H.sub.7                                                                          ##STR302##        H                                              n-C.sub.3 H.sub.7                                                                          ##STR303##        F                                              n-C.sub.5 H.sub.11                                                                         ##STR304##        H                                              n-C.sub.5 H.sub.11                                                                         ##STR305##        F                                              H.sub.2 CCH                                                                                ##STR306##        H                                              H.sub.2 CCH                                                                                ##STR307##        F                                              ______________________________________                                    

EXAMPLE 4

0.2 mol of I are stirred at 120° C. for 24 hours in 350 ml of anhydroushydrogen fluoride in a Hostalloy autoclave. After the mixture has beencooled to 0° C., ice-water and dichloromethane are added. The organicphase is separated off, washed with water, 10% sodium hydroxide solutionand again with water and evaporated in vacuo. The residue ischromatographed on a silica-gel column using hexane. Clp._(extr). =40;Δε=16.5; Δn=+0.125.

The following compounds of the formula ##STR308## are preparedanalogously:

    ______________________________________                                        A.sup.2 -Z.sup.2 -    L.sup.1                                                                             L.sup.2                                                                           L.sup.3                                       ______________________________________                                        C.sub.2 H.sub.5                                                                      ##STR309##     H     H   H                                             C.sub.2 H.sub.5                                                                      ##STR310##     H     H   F                                             C.sub.2 H.sub.5                                                                      ##STR311##     F     H   H                                             C.sub.2 H.sub.5                                                                      ##STR312##     F     F   H                                             C.sub.2 H.sub.5                                                                      ##STR313##     F     H   F                                             C.sub.2 H.sub.5                                                                      ##STR314##     F     F   F                                             n-C.sub.3 H.sub.7                                                                    ##STR315##     H     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR316##     H     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR317##     F     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR318##     F     F   H   Clp. = 92° C.; Δn =                                              +0.136; Δε = 15             n-C.sub.3 H.sub.7                                                                    ##STR319##     F     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR320##     F     F   F   Clp..sub.ark = 35° C.;                                                 Δn = +0.127; Δε =                                         7                                         n-C.sub.5 H.sub.11                                                                   ##STR321##     H     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR322##     F     H   H                                             n-C.sub.5 H.sub.11                                                                   ##STR323##     F     F   H                                             n-C.sub.5 H.sub.11                                                                   ##STR324##     F     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR325##     H     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR326##     H     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR327##     H     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR328##     F     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR329##     F     F   H                                             n-C.sub.6 H.sub.13                                                                   ##STR330##     F     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR331##     F     F   F                                             C.sub.2 H.sub.5                                                                      ##STR332##     H     H   H                                             C.sub.2 H.sub.5                                                                      ##STR333##     H     H   F                                             C.sub.2 H.sub.5                                                                      ##STR334##     F     H   H                                             C.sub.2 H.sub.5                                                                      ##STR335##     F     F   H                                             C.sub.2 H.sub.5                                                                      ##STR336##     F     H   F                                             C.sub.2 H.sub.5                                                                      ##STR337##     F     F   F                                             n-C.sub.3 H.sub.7                                                                    ##STR338##     H     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR339##     H     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR340##     F     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR341##     F     F   H                                             n-C.sub.3 H.sub.7                                                                    ##STR342##     F     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR343##     F     F   F                                             n-C.sub.5 H.sub.11                                                                   ##STR344##     H     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR345##     F     H   H                                             n-C.sub.5 H.sub.11                                                                   ##STR346##     F     F   H                                             n-C.sub.5 H.sub.11                                                                   ##STR347##     F     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR348##     F     F   F                                             n-C.sub.6 H.sub.13                                                                   ##STR349##     H     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR350##     H     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR351##     F     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR352##     F     F   H                                             n-C.sub.6 H.sub.13                                                                   ##STR353##     F     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR354##     F     F   F                                             C.sub.2 H.sub.5                                                                      ##STR355##     H     H   H                                             C.sub.2 H.sub.5                                                                      ##STR356##     H     H   F                                             C.sub.2 H.sub.5                                                                      ##STR357##     F     H   H                                             C.sub.2 H.sub.5                                                                      ##STR358##     F     F   H                                             C.sub.2 H.sub.5                                                                      ##STR359##     F     H   F                                             C.sub.2 H.sub.5                                                                      ##STR360##     F     F   F                                             n-C.sub.3 H.sub.7                                                                    ##STR361##     H     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR362##     H     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR363##     F     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR364##     F     F   H                                             n-C.sub.3 H.sub.7                                                                    ##STR365##     F     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR366##     F     F   F                                             n-C.sub.5 H.sub.11                                                                   ##STR367##     H     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR368##     F     H   H                                             n-C.sub.5 H.sub.11                                                                   ##STR369##     F     F   H                                             n-C.sub.5 H.sub.11                                                                   ##STR370##     F     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR371##     F     F   F                                             n-C.sub.6 H.sub.13                                                                   ##STR372##     H     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR373##     H     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR374##     F     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR375##     F     F   H                                             n-C.sub.6 H.sub.13                                                                   ##STR376##     F     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR377##     F     F   F                                             C.sub.2 H.sub.5                                                                      ##STR378##     H     H   H                                             C.sub.2 H.sub.5                                                                      ##STR379##     H     H   F                                             C.sub.2 H.sub.5                                                                      ##STR380##     F     H   H                                             C.sub.2 H.sub.5                                                                      ##STR381##     F     F   H                                             C.sub.2 H.sub.5                                                                      ##STR382##     F     H   F                                             C.sub.2 H.sub.5                                                                      ##STR383##     F     F   F                                             n-C.sub.3 H.sub.7                                                                    ##STR384##     H     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR385##     H     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR386##     F     H   H                                             n-C.sub.3 H.sub.7                                                                    ##STR387##     F     F   H                                             n-C.sub.3 H.sub.7                                                                    ##STR388##     F     H   F                                             n-C.sub.3 H.sub.7                                                                    ##STR389##     F     F   F                                             n-C.sub.5 H.sub.11                                                                   ##STR390##     H     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR391##     F     H   H                                             n-C.sub.5 H.sub.11                                                                   ##STR392##     F     F   H                                             n-C.sub.5 H.sub.11                                                                   ##STR393##     F     H   F                                             n-C.sub.5 H.sub.11                                                                   ##STR394##     F     F   F                                             n-C.sub.6 H.sub.13                                                                   ##STR395##     H     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR396##     H     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR397##     F     H   H                                             n-C.sub.6 H.sub.13                                                                   ##STR398##     F     F   H                                             n-C.sub.6 H.sub.13                                                                   ##STR399##     F     H   F                                             n-C.sub.6 H.sub.13                                                                   ##STR400##     F     F   F                                             ______________________________________                                    

Mixture examples

    ______________________________________                                        Example A                                                                     PCH-5F      9.0%     Clearing point  °C.!                                                                 88                                         PCH-6F      7.2%     Δn  589 nm, 20° C.!                                                            0.1001                                     PCH-7F      5.4%     Δε  1 kHz, 20° C.!                                                     6.4                                        CCP-20CF.sub.3                                                                            7.2%     V.sub.(10,0,20)  V!                                                                         1.85                                       CCP-30CF.sub.3                                                                            10.8%                                                             CCP-40CF.sub.3                                                                            8.1%                                                              CCP-50CF.sub.3                                                                            8.1%                                                              BCH-3F.F    10.8%                                                             BCH-5F.F    9.0%                                                              ECCP-30CF.sub.3                                                                           4.5%                                                              ECCP-50CF.sub.3                                                                           4.5%                                                              CBC-33F     1.8%                                                              CBC-53F     1.8%                                                              CUU-3-OMD   10.0%                                                             Example B                                                                     PCH-5F      9.0%     Clearing point  °C.!                                                                 88                                         PCH-6F      7.2%     Δn  589 nm, 20° C.!                                                            0.0998                                     PCH-7F      5.4%     Δε  1 kHz, 20° C.!                                                     6.4                                        CCP-20CF.sub.3                                                                            7.2%     V.sub.(10,0,20)  V!                                                                         1.89                                       CCP-30CF.sub.3                                                                            10.8%                                                             CCP-40CF.sub.3                                                                            8.1%                                                              CCP-50CF.sub.3                                                                            8.1%                                                              BCH-3F.F    10.8%                                                             BCH-5F.F    9.0%                                                              ECCP-30CF.sub.3                                                                           4.5%                                                              ECCP-50CF.sub.3                                                                           4.5%                                                              CBC-33F     1.8%                                                              CBC-53F     1.8%                                                              CUU-5-OMD   10.0%                                                             Example C                                                                     PCH-5F      9.0%     Clearing point  °C.!                                                                 90.5                                       PCH-6F      7.2%     Δn  589 nm, 20° C.!                                                            0.1009                                     PCH-7F      5.4%     Δε  1 kHz, 20° C.!                                                     6.2                                        CCP-20CF.sub.3                                                                            7.2%     V.sub.(10,0,20)  V!                                                                         1.94                                       CCP-30CF.sub.3                                                                            10.8%                                                             CCP-40CF.sub.3                                                                            8.1%                                                              CCP-50CF.sub.3                                                                            8.1%                                                              BCH-3F.F    10.8%                                                             BCH-5F.F    9.0%                                                              ECCP-30CF.sub.3                                                                           4.5%                                                              ECCP-50CF.sub.3                                                                           4.5%                                                              CBC-33F     1.8%                                                              CBC-53F     1.8%                                                              CGU-3-OMD   10.0%                                                             ______________________________________                                    

We claim:
 1. A compound of the formula I ##STR401## in which R is H, analkyl or alkenyl radical having 1 to 15 carbon atoms which isunsubstituted or monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen, one or more CH₂ groups in these radicalsoptionally being replaced, in each case independently of one another, by--O--, --S--, ##STR402## --CO--, --CO--O--, --O--CO-- or --O--CO--O-- insuch a manner that O atoms are not linked directly to one another,A¹ andA² are each, independently of one another,(a) a trans-1,4-cyclohexyleneradical in which each of one or two nonadjacent CH₂ groups areoptionally replaced by --O-- or --S--, (b) a 1,4-phenylene radical inwhich one or two CH groups are optionally replaced by N, (c) a radicalfrom the group consisting of 1,4-cyclohexylene, 1,4-bicyclo2.2.2!octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl,the radicals (a) and (b)optionally being substituted by one or two fluorine atoms, Z¹ and Z² areeach, independently of one another, --CO--O--, --O--CO--, --CH₂ O--,--OCH₂ --, --CH₂ CH₂ --, --CH═CH--, --C.tbd.C-- or a single bond, andone of the radicals Z¹ and Z² is alternatively --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --, and Q is --CHF-- or --CF₂ --, Y is a --CH₃, --CH₂ CH₃,--CHF₂, --CH₂ CF₃ or --CF₂ --CHF₂ group or, when Q is --CHF-- also a--CF₃ group, L¹, L² and L³ are each, independently of one another, H orF, and m is 0, 1 or
 2. 2. A compound of claim 1 of the formula I2##STR403## in which R, Q and Y are as defined in claim
 1. 3. A compoundof claim 1 of the formula ##STR404## in which R, Q and Y are as definedin claim 1, and L is H or F.
 4. A compound of claim 1 of the formula I5##STR405## in which R, Q and Y are as defined in claim
 1. 5. A compoundaccording to one of claim 1, in which Q--Y is CHF--CHF₂, CF₂ --CH₂--CF₃, CF₂ --CH₃, CF₂ --CH₂ --CHF₂, CHF--CF₂ --CHF₂ or CF₂ --CH₂ --CHF₂.6. A liquid-crystalline medium comprising at least twoliquid-crystalline components wherein at least one of the components isa compound of the formula I of claim
 1. 7. A liquid-crystal displayelement comprising a liquid-crystalline medium according to claim
 6. 8.An electro-optical display element comprising, as a dielectric, aliquid-crystalline medium according to claim
 6. 9. A compound of claim1, wherein m is
 0. 10. A compound of claim 1, wherein L³ is fluorine.11. A compound of claim 1, wherein each of L¹, L² and L³ are fluorine.12. A compound of claim 1, wherein R is alkyl or alkoxy.
 13. A compoundof claim 1, wherein A¹ and A² are independently 1,4-phenylene optionallymonosubstituted or disubstituted by F or mono-substituted by CN.
 14. Acompound of claim 1 which exhibits a dielectric anisotropy, Δε, of from15-20.
 15. The compound of claim 1, wherein L¹ and L² are each F.
 16. Acompound of the formula ##STR406## in which R is H, an alkyl or alkenylradical having 1 to 15 carbon atoms which is unsubstituted ormonosubstituted by CN or CF₃ or at least monosubstituted by halogen, oneor more CH₂ groups in these radicals optionally being replaced, in eachcase independently of one another, by --O--, --S--, ##STR407## --CO--,--CO--O--, --O--CO-- or --O--CO--O-- in such a manner that O atoms arenot linked directly to one another, ##STR408## and Q--Y is CHF--CHF₂ orCF₂ --CH₂ --CF₃.